Radio-frequency transformer



24, 1946- J. E. TILLMAN 01 RADIO FREQUENCY TRANSFORMER Filed Jan. 27, 1943 2 Sheets-Sheet l PiQI.

Inventor: John E. Tillman,

His Attorney.

Dec. 24, 1946. J. E. TILLMAN RADIO FREQUENCY TRANSFORMER Filed Jan. '27, 1943 2 sneaks-sheet 2 5 Fig.6.

W VIII/Ill Inventor: John E.Tillman,

His Attorney.

Patented Dec. 24, 1946 FiQE 2,413.2llli RADIO-FBEQFJENCY TRANSFGRMER John E. Tillman, Stratford, Gonn assignor to General Electric flompany. a corporation at New York Application January at, 1943, Serial No. static is Claims. (on. iii-s42) My invention relates to radio receiving apparatus and it has for its object to provide an im-= proved radio frequency transformer for such apparatus.

My invention relates more particularly to a powdered iron transformer for use at radio .'Tre-= quencles. It is desirable that such a transformer be both unitary in structure, in order to reduce manufacturing costs to a minimum and for ease of installation, and substantially sell-shielding to eliminate need for aluminum or copper shields and to provide increased gain without any amount of feedback. Another object of my invention, therefore, is to provide an improved radio frequency transformer whichis unitary in structure and substantially self-shielding.

A. further object is toprovide an improved transformer in which the mutual inductance of the windings thereof may readily be adjusted over a substantial range.

Still a further object is to provide an improved radio frequency transformer having high quality circuits with very little feedback to other circuits of the receiver.

An important feature or my invention is the use of a powdered iron body member having a plurality of chambers for the reception or trans= former windings, said chambers having a com. mon wall, and adjustable closure members for the chambers, adjustment of the position of the closure members being effective to control the mutual flux linkages of the windings without appreciably affecting the self inductance of the individual windings.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itseli, however, both as to its organization and method oi operation, together with further objects and ad= vantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings, in which Fig. 1 is a side elevation view partly in section of a transformer embodying my inven= tion; Fig. 2 is a plan view of the transformer of Fig. 1 along the line 2-2; Figs. 3 and 4 are views of certain elements of the transformer of Fig. 1; Figs. 5, 6, 7, and 8 show modifications of the elements of Fig. 3; and Fig. 9 represents a portion of a receiver circuit embodying the transformer of my invention.

Referring to Fig. l, I have shown a radio frequency transformer having a main body member It. The body member ill preferably is formed as a unitary structure by molding or compressing 2 and machining powdered iron particles. The member it has two recesses or cups i l and these recesses preferably being substantially ey lindrlcal in shape, so that a longitudinal cross section of the body member it, as seen in l, is in the form of a l having a mid-sec 118, which forms a common wall or leg for recesses ii and it, two end walls or legs i5, and a base portion lb. The base p 66 has two cylindrical openings it and 1 in coaxial respectively with the cyllndr' r cesses or wells it and 92. The cylindrical open" ings it and 68 have shoulder portions it and for the reception of the lower ends of tubular forms 26 and 32 upon which are wound the transformer windings 28 and 2t. Forms 2i and preferably are oi an. insulating material the synthetic resin type, although any other hill suitable dielectric material may be used.

The open ends of the recesses ii and iii are provided with closure members which comprise the hat, substantially circular washers 25 and 26 formed from compressed or molded powdered iron particles, and tapered or beveled shoulders ill and 28 are provided in the upper portion of the wall members of the body member ill for supporting these closure members. Members 25 and 2t; likewise have central openings 29 and 3t provided with shoulders 8i and 82: for the purpose of receiving the upper ends of forms 2! and 222 and supporting these forms rigidly in a central position within the recesses M and it. One side of each of the closure members to and 2b is cut away so that, in plan view, these mem here. as seen in Fig. 3, appear as circle having a segment removed. The purpose of forming the members and 2b as segmented circles with chords or cut-oil edges 33 and lid is explained in detail later. The members 25 and 26 are likewise preferably provided with beveled edges 35 in order to insure a close fitting of these edges with the shoulders 2i and 28.

Means for adjusting the inductance of the coils or windings 23 and Zilof the transformer to a desired value is provided by the powdered iron cores All and (it adjustably disposed within the dorms 2i and 22, slots 32 and 58 being provided at the, bottom of these cores fill and (ii respec= tively for adjustment of the position of the cores within the windings of the transformer in a manner to be explained later.

The transformer body it may be supported I from a radio chassis Ml by means of bolts which pass through the holes it provided in main. body it for this purpose. A mounting B remainssubstantially constant.

board 47 of insulating material is provided below' being provided between the nut 8 and chassis M and between the head of bolt 45 and the bottom wall iii of the transformer body I0. Chassis 46 is provided with a pair of openings 50, overlying the wells II and I2 of the transformer, through which open'ings extend the terminal posts 5| riveted to the mounting board 41 in the usual manner and grooves or slots 52 are provided in the washers 25-and 26 for passing the leads of windings 23 and 24 to the said terminal posts. Nuts 53 are likewise riveted to mounting board 41 in a well known manner and provide means for threadedly engaging screws 52 having one of their ends embedded in tuning cores 40 and Ill, so that by means of slots 42v and 43 in the bottom surfaces of these cores the ,cores may be raised or lowered within the 4 and 26 does not affect the reluctance of the paths for the normal lines of flux B of the windings 23 and 24, the above described adjustment of mutual inductance of the transformer windings is obtained with substantially no change in the self inductance of these windings.

After final adjustment of the positions of the washers 25 and 26 for adjusting the mutual inductance is determined, the wells H and I2 may be filled with any suitable sealing material, such as wax, for holding the transformer windings and the washers securely in place. Any further adjustment of the frequency of the transformers is made thereafter by adjustment of the position of iron cores 40 and M with respect to the windings of the transformer to tune these windings to exact resonance with the capacitance of the windings of the transformer for tuning the windings in the usual manner.

The operation of the transformer described will be discussed with'particular reference to its use as an intermediate frequency transformer in a radio receiver of the superheterodyne type. In Fig. 1 there are shown two dotted paths A and B to designate the paths of fluxlines in the transformer housing. The flux lines B, which for winding 23, for example, flow from the core member 60 through the washer to the side wall Ill and the center wall l3, arethe normal lines for the winding 23 and are confined to the core 40 and the adjacent half of the housing. The number of flux lines B for a given transformer core and windings is determined by the position of tuning cores 80' and 4-1. AdJustment of the position of these cores with respect to their corresponding windings is effective to vary the self inductance of the coils 23 and 24 until desired values of inductance for these coils is obtained.

The flux lines A are those lines of flux which return to the core 40 through the core M, rather than the wall of the housing, and form a common linkage, or coupling, of the windings 23 and 24. It is seen that an increase in the thickness of the common wall l3 results in a smaller proportion of flux lines A in relation to the number of flux lines B, while the path of flux lines B remains essentially the same. The mutual coupling of the windings 23 and 24, therefore, is

determined primarily by the thickness of the common wall l3 between recesses l I and 12 in th transformer body. If a higher reluctance material, such as an air gap, is introduced into the path A, it results in a decrease in the proportion of flux lines A to flux lines B and magnetically makes the path A longer while the length of path Final adjustment of the mutual inductance of windings 23 and 24 is made, therefore, by rotation of the washers or closure members 25 and 26, having cut-away portions, thereby to vary the air gap between'the edges or chords 33 and 34 and the common wall l3. By selection of the height of the segment cut off from the washers 25 and 26, the range of variation of mutual inductance is determined. This range may bemade very narrow or quite broad so that rotation of the washers may be effective to vary the coupling between the windings from very loose to very close coupling. Furthermore, since rotation of the washers 25 Fri respective circuits at a desired frequency.

In connecting the transformer into a radio circuit, the leads from the transformer windings to the circuits of the receiver are made as short as possible to reduce the amount of feedback to other stages of the receiver circuit. Since the transformer windings are substantially shielded, by the previously described structure, from the remaining circuits of the receiver, by proper precautions with respect to connecting leads, the inductance of the individual windings and hence the quality of the tuned circuits of the transformer may be made quite large without the introduction of any substantial amount of feedback.

In the construction of the main body III, the tuning cores 40 and Al, and the tuning washers 25 and 25, which also function as pole pieces for cores Q0, and 8|, it is preferable to use powdered iron particles having low resistance and high conductance, since better electrostatic shielding may be obtained if the particles are uninsulated from each other and are compressed, or otherwise molded, by any suitable method known in the art.

Modifications of the form of the closur members 25 and 26 are shown in Figs. 5-8. In "Figs. 5 and 6 is shown a closure member 60 having a portion SI of reduced thickness. When such a closure member is used, rotation of the member with respect to the shoulders of the transformer main core l0 permits variation of the reluctance of the path between the cores 40 and 4|. In the washer 62' of Fig. 7, a large portion of the material has been cut away so that very large adjustment of the mutual inductance of the transformer is effected by rotation of this washer with respect to the common wall. In Fig, 8, the washer 64 is provided with an insert of nonmagnetic or insulating material to permit variation of the reluctance of the flux path A between tuning cores 40 and 4|. Th structures of Figs. 5, 6, and 8 provide particularly good shielding of the transformer windings so that transformers using this type of closure washers may be employed without the necessity of using the chassis for additional shielding.

InFig. 9 my transformer is illustrated as coupling two electron discharge devices 10 and 1B.

aerosol is not shown but merely indicated by the legend 3+, through the decoupling filter comprising re sistance l5 and capacitor 18. The tuned secondary circuit comprising winding l! of transiiormerlt and capacitance 8!, is connected to the control electrode of amplifying device it, the anode of which is connected by means of lead it to succeeding stages of the receiver circuit, Transformer i3 is of the type illustrated in Fig. l and described above and arrows 80 indicate that it is adjustable for both self and mutual inductance in accordance with my invention.

While I have shown a particular embodiment of my invention, it wili'of course be understood that I do not wish to be limited thereto since various modifications may be made, and Icontemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A radio frequency transformer comprising a body member of magnetic material having a plurality of recesses therein, said recesses being separated by a wall ofsaid body, each or said recesses having a corresponding winding of said transformer positioned therein, said windings being tuned to a desired frequency, and magnetic closure members for said recesses, each magnetic closure member partially magnetically closing the respective recess and being arranged to vary in position to control the reluctance of the hut: path and the coupling between different of said windings without changing materially the reluctance orthe flux path and the self-inductance or the individual windings.

2. A radio frequency transformer comprising a body member of magnetic material having a plurality of recesses therein, said recesses being separated by a wall of said body, each oi said recesses having corresponding winding of said transformer positioned therein, said windings be ing tuned to a desired frequency, and magnetic closure members for said recess, said windings producing flux traversing a path comprising the respective closure member and said common wall, and said closure members individually being ar ranged to vary in position to control the reluct ance of said flux paths and the mutual inductance of said windings without varying the reluctance of the flux path and the self-=inductance of the associated windings.

a transformer for radio frequency currents comprising, a unitary magnetic body member, said body member having a pair of recesses and a wail of magnetic material therebetween, a magnetic core centrally disposed within each or said recesses, a winding disposed within each of said recesses and encircling said core, said cores form ing a path for iiux mutual to said windings, and means for controlling the mutual flux linkages of said windings, said means comprising a circular closure member for each of said recesses, each closure member having a segment removed there= from and being rotatably supported at the entrance to a respective one of said recesses.

i. The combination, in a transformer for radio frequency currents, of a magnetic body member having a pair or substantially cylindrical recesses therein and a wall therebetween, a magnetic core centrally disposed within each of said recesses, a winding disposed within each of said recessesand encircling said core, said cores forming a path for flllli mutual to the windings in both of said recesses; and means for controlling the flux ilow= and substantially coplanar entrances separated- 'by said wall portion, a magnetic core member centrally disposed within each of said recesses, a

' winding disposed within each of said recesses and encircling said core, said cores forming a path for flux mutual to the windings in both or said recesses, and a. closure member rotatably supported in substantially the same plane across each of said entrances, said closure members being formed of magnetic material of such shape that rotation of said closure members in said plane is effective to change the reluctance of the path between said cores and vary the mutual flux or said transformer windings.

6. A transformer for high frequency currents comprising, a magnetic body member, said body member having a pair of wells therein separated by a wall and each of said wells having substantially coplanar entrances separated by said wall, a magnetic core member centrally disposed within each of said wells, a winding disposed within each of said wells and encircling said core member, magnetic pole pieces movably supported in said entrances, and means whereby said core members may be moved with respect to said windings and said pole pieces thereby to adjust the self inductance of said windings, said pole pieces and said core members forming a path for flux mutual to said windings and movement of said pole pieces in the plane of said entrances being effective to adjust the mutual inductance of said windings without changing substantially their self inductance.

"7. A transformer core comprising a powdered iron body member, said body member having a pair of chambers therein separated by a common wall, each of said chambers having an open end whereby a winding may be placed in each of said chambers, and an adjustable closure member for each of said open ends, said closure members having portions of difierent magnetic reluctance, whereby separate adjustment of the position of each of said closure members with respect to said wall is effective to control the reluctance of the flux path between said windings without changing materially the reluctance of the flux path of the individual windings.

ii. The combination, in a high frequency transformer, of primary and secondary windings ranged on respective parallel axes, a core comprising respective parallel legs positioned respectively along and coincident with the axis of a respective one of said windings and a leg parallel with said first legs positioned between said windings, said legs being magnetically joined by a yoke at one end of each winding, and a second yolre member movable in a plane at right angles to said legs at the opposite ends of said windings and arranged to vary the reluctance of the flux path between said windings without changing materially the reluctance of the flux path of the individual windings.

9. Thecombination, in a high frequency trans- 7 former, of primary and secondary windings arranged on respective parallel axes, a core having respective parallel legs including legs adjustable in position along the axis of a respective one of said windings, and a leg between said windings, said legs being magnetically joined by a yoke at one end of each winding, and a core member movable in a plane at right angles to said legs at the opposite ends of said windings.

10. The combination, in a high frequency transformer, of primary and secondary windings arranged on respective parallel axes, a core having respective parallel legs including legs adjustable in position along the axis of a respective one of said windings, and a leg between said windings, said legs being magnetically joined by a yoke at one end of each winding, a core member movable in a plane at right angles to said legs at the opposite ends of said windings, means to vary the position of said first legs along said parallel axes to vary the self-inductance of the respective windings, and means to adjust the position of said last-mentioned core member to vary the mutual inductance of said windings.

11. The combination, in a high frequency transformer, of primary and secondary windings arranged on respective parallel axes, a core member comprising magnetic legs disposed along said axes, said windings at least partly encircling said legs, an intermediate magnetic leg positioned between said windings and forming a magnetic path common to both of said windings, additional respective magnetic legs arranged substantially parallel to said axes and positioned on the sides of said windings remote from said intermediate leg, all of said legs being joined magnetically by aaraaoi a yoke at one end of said windings, and a second yoke member movable in a plane at right angles to said legs at the opposite ends of said windings.

12. The combination, in a high frequency transformer, of primary and secondary windings arranged on respective parallel axes, a core member comprising magnetic legs disposed along said axes, said windings at least partly encircling said legs. an intermediate magnetic leg positioned between said windings and forming a magnetic path common to both of said windings, additional respective magnetic legs arranged substantially parallel to said axes and positioned on the sides of said windings remote from said intermediate leg, all of said legs being 'joined magnetically by a yoke at one end of said windings, a second yoke member movable in a plane at right angles to said legs at the opposite ends of said windings, said second yoke member being variable in position to vary the mutual inductance of said windings.

13. The combination, in a high frequency transformer, comprising a core having at least three parallel legs, aprimary winding and a secondary winding arranged on respective parallel axes between different pairs of said legs, a core member adjustable in position in each winding to vary the inductance of the respective winding, and means in addition to said core member to vary oppositely the magnetic reluctance of the 'fiux paths from each of said core members to the legs at the opposite sides of the respective JOHN EJTILLMAN. 

